Light-emitting device and illuminator

ABSTRACT

A light-emitting device, having high light extraction efficiency, capable of obtaining diffused light is obtained. This light-emitting device comprises a light-emitting diode, a portion, formed on a plane substantially parallel to a light-emitting surface of the light-emitting diode, having a dielectric constant periodically modulated with respect to the in-plane direction of the plane substantially parallel to the light-emitting surface and a member provided on the side of the light-emitting surface of the light-emitting diode for diffusing light emitted from the light-emitting diode.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a light-emitting device and anilluminator, and more particularly, it relates to a light-emittingdevice including a light-emitting diode and an illuminator employingthis light-emitting device.

[0003] 2. Description of the Background Art

[0004] A light-emitting diode mounted with a photonic crystal on itslight-emitting surface to be capable of improving efficiency forextracting light emitted from the light-emitting diode is known ingeneral. This type of light-emitting diode is disclosed in “Highlydirective light sources using two-dimensional photonic crystal slabs”,Applied Physics Letters, December 2001, Vol. 79, No. 26, pp. 4280-4282or “Strongly directional emission from AlGaAs/GaAs light-emittingdiodes”, Applied Physics Letters, November 1990, Vol. 57, No. 22, pp.2327-2329, for example.

[0005]FIG. 13 is a sectional view for illustrating the structure of aconventional light-emitting diode mounted with a photonic crystal on itslight-emitting surface. The structure of the conventional light-emittingdiode having the photonic crystal mounted on the light-emitting surfaceis now described with reference to FIG. 13.

[0006] In the conventional light-emitting diode having the photoniccrystal mounted on the light-emitting surface, an n-type cladding layer202 of n-type AlGaAs, an emission layer 203 of p-type GaAs and a p-typecladding layer 204 of p-type AlGaAs are successively stacked on ann-type GaAs substrate 201, as shown in FIG. 13. Thus, the light-emittingdiode has a double heterostructure. Periodically arranged striped(elongated) corrugation having a prescribed width and a prescribed depthare formed on the upper surface of the p-type cladding layer 204. Ametal layer 205 of Ag is formed on the upper surface of the p-typecladding layer 204 having the aforementioned corrugation.

[0007] In the conventional light-emitting diode, as hereinabovedescribed, the upper surface of the p-type cladding layer 204 is formedwith the periodically arranged striped corrugation having the prescribedwidth and the prescribed depth while the metal layer 205 is formed onthe upper surface of the p-type cladding layer 204 having thecorrugation, thereby forming a portion having a dielectric constantperiodically modulated with respect to the in-plane direction of thep-type cladding layer 204 and the metal layer 205. Thus, the p-typecladding layer 204 can also function as a photonic crystal.Consequently, the light-emitting diode emits light perpendicularly tothe light-emitting surface, and extraction efficiency for the emittedlight can be improved.

[0008] However, the aforementioned conventional light-emitting diodehaving the photonic crystal mounted on the light-emitting surface emitsthe light perpendicularly to the light-emitting surface, and hence it isdifficult to obtain diffused light suitable for indoor illumination orthe like. Therefore, it is disadvantageously difficult to apply theconventional light-emitting diode having the photonic crystal mounted onthe light-emitting surface to illumination.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a light-emittingdevice, having high light extraction efficiency, capable of obtainingdiffused light.

[0010] Another object of the present invention is to provide anilluminator having high light extraction efficiency.

[0011] In order to attain the aforementioned objects, a light-emittingdevice according to a first aspect of the present invention comprises alight-emitting diode, a portion, formed on a plane substantiallyparallel to a light-emitting surface of the light-emitting diode, havinga dielectric constant periodically modulated with respect to thein-plane direction of the plane substantially parallel to thelight-emitting surface and a member provided on the side of thelight-emitting surface of the light-emitting diode for diffusing lightemitted from the light-emitting diode.

[0012] In the light-emitting device according to the first aspect, ashereinabove described, the portion having the dielectric constantperiodically modulated with respect to the in-plane direction is formedon the plane substantially parallel to the light-emitting surface of thelight-emitting diode so that the light emitted from the light-emittingdevice can be parallelized perpendicularly to the light-emittingsurface, whereby the efficiency for extracting the light from thelight-emitting diode can be improved. The member diffusing the lightemitted from the light-emitting diode is provided on the side of thelight-emitting surface of the light-emitting diode so that the parallellight emitted from the light-emitting device can be diffused intovarious directions, whereby diffused light can be emitted. Thus, thelight-emitting device is improved in light extraction efficiency, andcan emit diffused light.

[0013] In the aforementioned light-emitting device according to thefirst aspect, the portion having the periodically modulated dielectricconstant may be constituted by periodically arranging materials havingdifferent dielectric constants, and the portion having the periodicallymodulated dielectric constant may consist of a photonic crystal.According to this structure, the portion having the periodicallymodulated dielectric constant can be easily obtained. The portion havingthe periodically modulated dielectric constant can be formed byperiodically arranging dielectric substances and air or by periodicallyarranging dielectric substances and vacuums.

[0014] In the aforementioned light-emitting device according to thefirst aspect, the member diffusing the emitted light is preferablyconductive. According to this structure, the light-emitting diode andthe member diffusing the emitted light can be electrically connectedwith each other when the light-emitting diode and the member diffusingthe emitted light are formed in close contact with each other. Thus, themember diffusing the emitted light can be formed with a part forintroducing current into the light-emitting diode, whereby thelight-emitting diode may not be directly wired. Consequently, thelight-emitting device is easy to assemble. Further, the light-emittingsurface may not be wired, whereby no wire blocks the emitted light.Consequently, the intensity of the light emitted from the light-emittingdevice can be improved.

[0015] In the light-emitting device including the aforementionedconductive member diffusing the emitted light, the conductive memberdiffusing the emitted light is preferably formed to be in contact with aportion of the light-emitting diode provided on the light-emitting side.According to this structure, the light-emitting diode and the memberdiffusing the emitted light can be easily electrically connected witheach other.

[0016] In the light-emitting device including the aforementionedconductive member diffusing the emitted light, the conductive memberdiffusing the emitted light preferably consists of at least one materialselected from a group consisting of n-type SiC, n-type AlN and p-typediamond. When made of such a material, the member diffusing the emittedlight can also attain excellent thermal conductivity in addition to theconductivity, thereby easily dissipating heat generated in thelight-emitting diode through the member diffusing the emitted light.Consequently, the light-emitting device can be driven with largercurrent, whereby the intensity of the emitted light can be improved.

[0017] In the aforementioned light-emitting device according to thefirst aspect, the member diffusing the emitted light may be constitutedof a lens. According to this structure, the parallel light emitted fromthe light-emitting diode can be easily converted to diffused light. Inthis case, the member diffusing the emitted light may include a concavelens. According to this structure, the parallel light emitted from thelight-emitting diode can be diffused through the concave lens, wherebythe parallel light can be easily converted to diffused light. In thiscase, the concave lens may include a plano-concave lens having a flatfirst surface and a concave second surface. The light-emitting devicemay be arranged in contact with the flat first surface. According tothis structure, the light-emitting device and the lens can be easilybonded to each other. In addition, the reflected light can be reduced onthe light-emitting surface of the light-emitting device and the flatfirst surface of the lens as compared with a case of arranging thelight-emitting device and the lens separately from each other.

[0018] Further, the concave lens may be arranged at ratio of one to aplurality of light-emitting diodes. Further, a plurality of concave lensand light-emitting diodes may be arranged in the form of an array.According to this structure, the sizes of regions for emitting light canbe increased. Thus, the light-emitting device can be easily used as alight source for illumination or the like.

[0019] In the aforementioned light-emitting device according to thefirst aspect, the member diffusing the emitted light may include aconvex mirror. According to this structure, the parallel light emittedfrom the light-emitting diode can be reflected and diffused by theconvex mirror, whereby the parallel light can be easily converted todiffused light.

[0020] In the aforementioned light-emitting device according to thefirst aspect, the member diffusing the emitted light may include atranslucent member dispersively containing a light diffusing agentconsisting of substantially transparent particulates. According to thisstructure, the parallel light emitted from the light-emitting diode canbe diffused with the translucent member dispersively containing thelight diffusing agent, whereby the parallel light can be easilyconverted to diffused light.

[0021] In the aforementioned light-emitting device according to thefirst aspect, the member diffusing the emitted light may include atranslucent member having fine corrugation at least either on the frontsurface or on the back surface. According to this structure, theparallel light emitted from the light-emitting diode can be diffusedwith the translucent member having the fine corrugation, whereby theparallel light can be easily converted to diffused light.

[0022] In the light-emitting device including the aforementionedtranslucent member having the fine corrugation, the interval betweenadjacent projecting portions in the fine corrugation may be at leastabout 200 nm and not more than about 2000 nm. When the interval betweenthe adjacent projecting portions is set in this range, the intervalcorresponds to a value equivalent to or several times the emissionwavelength, whereby the light can be diffused by a diffraction effect.

[0023] In the light-emitting device including the aforementionedtranslucent member having the fine corrugation, the interval betweenadjacent projecting portions in the fine corrugation may be at leastabout 2 μm and not more than about 100 μm. When the interval between theadjacent projecting portions is set in this range, the light can berefracted by the corrugation to be easily diffused.

[0024] The aforementioned light-emitting device according to the firstaspect preferably further comprises a fluorescent body provided betweenthe light-emitting surface and the member diffusing the emitted light.According to this structure, the fluorescent body scatters the emittedlight, whereby diffused light can be more easily obtained. Further, thewavelength of the light emitted from the light-emitting diode can beconverted to a different wavelength, whereby white light suitable forillumination can be obtained when various fluorescent bodies arecombined with each other.

[0025] In the aforementioned light-emitting device according to thefirst aspect, the light-emitting diode preferably includes an emissionlayer, and the emission layer preferably consists of a nitride-basedsemiconductor. According to this structure, high-energy light can beeasily obtained at a short wavelength in the blue to ultraviolet range,whereby the intensity of the emitted light can be improved.

[0026] In the aforementioned light-emitting device according to thefirst aspect, a plurality of light-emitting diodes are preferablyarranged in the form of a matrix in plane. According to this structure,the size of a region for emitting the light can be so increased that thelight-emitting device can be easily used as a light source forillumination or the like.

[0027] In this case, the member diffusing the emitted light preferablyincludes a lens, and a plurality of such lenses are preferably arrangedin the form of a matrix in plane. According to this structure, lightemitted from light-emitting diodes arranged in the form of a matrix canbe easily diffused.

[0028] A light-emitting device according to a second aspect of thepresent invention comprises a light-emitting diode, a portion, formed ona plane substantially parallel to a light-emitting surface of thelight-emitting diode, having a dielectric constant periodicallymodulated with respect to the in-plane direction of the planesubstantially parallel to the light-emitting surface and means providedon the side of the light-emitting surface of the light-emitting diodefor diffusing light emitted from the light-emitting diode.

[0029] In the light-emitting device according to the second aspect, ashereinabove described, the portion having the dielectric constantperiodically modulated with respect to the in-plane direction is formedon the plane substantially parallel to the light-emitting surface of thelight-emitting diode so that the light emitted from the light-emittingdevice can be parallelized perpendicularly to the light-emittingsurface, whereby efficiency for extracting the light from thelight-emitting diode can be improved. Further, the means diffusing thelight emitted from the light-emitting diode is provided on the side ofthe light-emitting surface of the light-emitting diode so that theparallel light emitted from the light-emitting device can be diffused invarious directions, whereby diffused light can be emitted. Thus, thelight-emitting device is improved in light extraction efficiency, andcan emit diffused light.

[0030] An illuminator according to a third aspect of the presentinvention comprises a light-emitting device including a light-emittingdiode, a portion, formed on a plane substantially parallel to alight-emitting surface of the light-emitting diode, having a dielectricconstant periodically modulated with respect to the in-plane directionof the plane substantially parallel to the light-emitting surface and amember provided on the side of the light-emitting surface of thelight-emitting diode for diffusing light emitted from the light-emittingdiode.

[0031] In the illuminator according to the third aspect, as hereinabovedescribed, the portion having the dielectric constant periodicallymodulated with respect to the in-plane direction is formed on the planesubstantially parallel to the light-emitting surface of thelight-emitting diode so that the light emitted from the light-emittingdevice can be parallelized perpendicularly to the light-emittingsurface, whereby efficiency for extracting the light from thelight-emitting diode can be improved. The member diffusing the lightemitted from the light-emitting diode is provided on the side of thelight-emitting surface of the light-emitting diode so that the parallellight emitted from the light-emitting device can be diffused intovarious directions, whereby diffused light can be emitted. Thus, thelight-emitting device is improved in light extraction efficiency and canemit diffused light, whereby the illuminator can attain a sufficientquantity of light by employing this light-emitting device as a lightsource.

[0032] The aforementioned illuminator according to the third aspectpreferably further comprises a fluorescent body arranged at a prescribedinterval from the light-emitting device for converting the light emittedfrom the light-emitting device to white light. According to thisstructure, white light suitable for the illuminator can be easilyobtained. In this case, the fluorescent body may be formed by mixingfluorescent materials having a plurality of emission colors with eachother.

[0033] In the aforementioned illuminator according to the third aspect,a plurality of light-emitting diodes constituting the light-emittingdevice are preferably arranged in the form of a matrix in plane.According to this structure, the size of a region emitting the light canbe so increased that the light-emitting device can be easily used as thelight source for the illuminator. In this case, the member diffusing theemitted light preferably includes a lens, and a plurality of such lensesare preferably arranged in the form of a matrix in plane. According tothis structure, light emitted from light-emitting diodes arranged in theform of a matrix can be easily diffused.

[0034] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a sectional view for illustrating the structure of alight-emitting device according to a first embodiment of the presentinvention;

[0036]FIG. 2 is a top plan view for illustrating the planar structure ofa p-type contact layer according to the first embodiment of the presentinvention;

[0037]FIG. 3 is a sectional view for illustrating the structure of alight-emitting device according to a second embodiment of the presentinvention;

[0038]FIG. 4 is a top plan view for illustrating the planar structure ofa metal contact layer according to the second embodiment of the presentinvention;

[0039]FIG. 5 is a sectional view for illustrating a process offabricating the light-emitting device according to the second embodimentshown in FIG. 3;

[0040]FIG. 6 is a sectional view for illustrating the structure of anilluminator employing a light-emitting device according to a thirdembodiment of the present invention;

[0041]FIG. 7 is a sectional view for illustrating the structure of alight-emitting device according to a fourth embodiment of the presentinvention;

[0042]FIG. 8 is a plan view for illustrating the structure of alight-emitting device according to a fifth embodiment of the presentinvention;

[0043]FIG. 9 is a sectional view for illustrating the structure of thelight-emitting device according to the fifth embodiment of the presentinvention;

[0044]FIG. 10 is a sectional view for illustrating the structure of alight-emitting device according to a sixth embodiment of the presentinvention;

[0045]FIG. 11 is a sectional view for illustrating the structure of alight-emitting device according to a seventh embodiment of the presentinvention;

[0046]FIG. 12 is a sectional view for illustrating the structure of anilluminator employing a light-emitting device according to an eighthembodiment of the present invention; and

[0047]FIG. 13 is a sectional view for illustrating the structure of alight-emitting diode (light-emitting device) having a photonic crystalmounted on a light-emitting surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Embodiments of the present invention are now described withreference to the drawings.

First Embodiment

[0049] The structure of a light-emitting device 10 according to a firstembodiment of the present invention is described with reference to FIGS.1 and 2. The light-emitting device 10 according to the first embodimentincludes a light-emitting diode and a plano-concave lens 50.

[0050] In the light-emitting diode according to the first embodiment, asingle-crystalline GaN layer 4, doped with Si, having a thickness ofabout 5 μm is formed on the (0001) plane of an n-type GaN substrate 1,doped with oxygen or Si, of about 2 mm square having a thickness ofabout 200 μm to about 400 μm. An n-type cladding layer 6 ofsingle-crystalline n-type Al_(0.1)Ga_(0.9)N, doped with Si, having athickness of about 0.15 μm is formed on the n-type GaN layer 4. Anactive layer 7 having a multiple quantum well (MQW) structure obtainedby alternately stacking six barrier layers of single-crystalline undopedGaN each having a thickness of about 5 nm and five well layers ofsingle-crystalline undoped Ga_(0.9)In_(0.1)N each having a thickness ofabout 5 nm is formed on the n-type cladding layer 6. A protective layer8 of single-crystalline undoped GaN having a thickness of about 10 nmand a p-type cladding layer 9 of single-crystalline p-typeAl_(0.1)Ga_(0.9)N, doped with Mg, having a thickness of about 0.15 μmare formed on the active layer 7 in this order.

[0051] A p-type contact layer 11 of single-crystalline p-typeGa_(0.95)In_(0.05)N having a thickness of about 30 nm is formed on theupper surface of the p-type cladding layer 9. As shown in FIG. 2, thep-type contact layer 11 is formed therein with a plurality of circularthrough holes 11 a, each having a diameter of about 250 nm, arranged ina two-dimensional triangle lattice at an interval (D) of about 380 nmsubstantially equal to about {fraction (4/3)}^(1/2) times the emissionwavelength λ in the p-type cladding layer 9. The p-type contact layer 11having the through holes 11 a is an example of the “portion having adielectric constant periodically modulated with respect to the in-planedirection of said plane substantially parallel to said light-emittingsurface” in the present invention.

[0052] According to the first embodiment, the interval (D) is designedassuming that the peak emission wavelength λ of light emitted from anemission layer (active layer 7) is about 380 nm and the refractive indexof a nitride-based semiconductor is 2.3. While the interval (D) ispreferably designed to be about ⅔^(1/2) times the emission wavelength λin the p-type cladding layer 9, precise processing is required in thiscase. According to the first embodiment, therefore, the interval (D) isdesigned to correspond to about {fraction (4/3)}^(1/2) times theemission wavelength k in the p-type cladding layer 9, in order tofurther simplify the processing.

[0053] A p-side electrode 12 is formed on the upper surface of thep-type contact layer 11, to fill up the through holes 11 a of the p-typecontact layer 11. This p-side electrode 12 is constituted of an ohmicelectrode layer of about 2 nm in thickness consisting of an Ni layer, aPd layer or a Pt layer, an oxide transparent electrode layer of indiumtin oxide (ITO) having a thickness of about 200 nm, a metal reflectinglayer of about 1 μm in thickness consisting of an Al layer, an Ag layeror an Rh layer, a barrier electrode consisting of a Pt layer or a Tilayer and a pad electrode consisting of an Au layer or an Au—Sn layer inascending order.

[0054] An n-side electrode 16 is formed on a region of about 50 μm inwidth along the outer peripheral portion of the back surface of then-type GaN substrate 1. The n-side electrode 16 is constituted of anohmic electrode layer consisting of an Al layer, a barrier electrodeconsisting of a Pt layer or a Ti layer and a pad electrode consisting ofan Au layer or an Au—Sn layer successively from the side closer to theback surface of the n-type GaN substrate 1. The light-emitting diode ofthe light-emitting device 10 according to the first embodiment has theaforementioned structure.

[0055] The plano-concave lens 50 consisting of a material such as n-typeSiC, n-type AlN or p-type diamond having excellent thermal conductivityand electrical conductivity is welded to the back surface of theaforementioned light-emitting diode. This plano-concave lens 50 iswelded to the n-side electrode 16 while directing the planar sidethereof toward the n-type GaN substrate 1. The plano-concave lens 50 isan example of the “member for diffusing light emitted from saidlight-emitting diode” or “means for diffusing light emitted from saidlight-emitting diode” in the present invention. The aforementionedlight-emitting diode and the plano-concave lens 50 constitute thelight-emitting device 10 according to the first embodiment shown in FIG.1.

[0056] In order to form an illuminator with the light-emitting device 10according to the first embodiment, the upper surface of the p-sideelectrode 12 of the aforementioned light-emitting diode is welded to asubmount (heat sink: not shown). In this case, the back surface of then-type GaN substrate 1 formed with the n-side electrode 16 serves as alight-emitting surface emitting light along arrow in FIG. 1.

[0057] A process of fabricating the light-emitting device 10 accordingto the first embodiment is described with reference to FIG. 1. First,the n-type GaN substrate 1, doped with oxygen or Si, of about 2 mmsquare having the thickness of about 200 μm to about 400 μm is prepared.The single-crystalline n-type GaN layer 4, doped with Si, having thethickness of about 5 μm is grown on the (0001) Ga plane of the n-typeGaN substrate 1, held at a temperature of about 1000° C. to about 1200°C., by MOVPE (metal organic vapor phase epitaxy) with carrier gasconsisting of an H₂/N₂ gas mixture containing about 50% of H₂, sourcegas consisting of NH₃ and trimethyl gallium (TMGa) and dopant gasconsisting of SiH₄ at a growth rate of about 3 μm/h.

[0058] Then, the n-type cladding layer 6 of single-crystalline n-typeAl_(0.1)Ga_(0.9)N, doped with Si, having the thickness of about 0.15 μmis grown on the n-type GaN layer 4 with carrier gas consisting of anH₂/N₂ gas mixture containing about 1% to about 3% of H₂, source gasconsisting of NH₃, TMGa and trimethyl aluminum (TMAl) and dopant gasconsisting of SiH₄ at a growth rate of about 3 μm/h. while keeping thetemperature of the n-type GaN substrate 1 at about 1000° C. to about1200° C., preferably at about 1150° C.

[0059] Then, the active layer 7 having the MQW structure obtained byalternately stacking the six barrier layers of single-crystallineundoped GaN each having the thickness of about 5 nm and the five welllayers of single-crystalline undoped Ga_(0.9)In_(0.1)N each having thethickness of about 5 nm is formed on the n-type cladding layer 6 withcarrier gas consisting of an H₂/N₂ gas mixture containing about 1% toabout 5% of H₂ and source gas consisting of NH₃, triethyl gallium (TEGa)and trimethyl indium (TMIn) at a growth rate of about 0.4 nm/s whilekeeping the temperature of the n-type GaN substrate 1 at about 700° C.to about 1000° C., preferably at about 850° C. In continuation, theprotective layer 8 of single-crystalline undoped GaN having thethickness of about 10 nm is grown at a growth rate of about 0.4 nm/s.

[0060] Then, the p-type cladding layer 9 of single-crystalline p-typeAl_(0.1)Ga_(0.9)N, doped with Mg, having the thickness of about 0.15 μmis grown on the protective layer 8 with carrier gas consisting of anH₂/N₂ gas mixture containing about 1% to about 3% of H₂, source gasconsisting of NH₃, TMGa and TMAl and dopant gas consisting ofbiscyclopentadienyl magnesium (Cp₂Mg) at a growth rate of about 3 μm/hwhile keeping the temperature of the n-type GaN substrate 1 at about1000° C. to about 1200° C., preferably at about 1150° C.

[0061] Then, cylindrical SiN layers (not shown) of about 250 nm indiameter arranged in a two-dimensional triangle lattice at an intervalof about 380 nm substantially equal to about {fraction (4/3)}^(1/2)times the emission wavelength λ in the p-type cladding layer 9 areformed by lithography employing electron beam or the like and etching.In other words, the cylindrical SiN layers are formed on positions to beformed with the through holes 11 a shown in FIG. 2. The SiN layers areemployed as masks for growing the p-type contact layer 11 ofsingle-crystalline p-type Ga_(0.95)In_(0.05)N having the thickness ofabout 30 nm on the p-type cladding layer 9 by MOVPE. At this time, thep-type contact layer 11 is formed with carrier gas consisting of anH₂/N₂ gas mixture containing about 1% to about 5% of H₂, source gasconsisting of NH₃, TMGa and TMIn and dopant gas consisting of Cp₂Mg at agrowth rate of about 0.4 nm/s while keeping the temperature of the GaNsubstrate 1 at about 700° C. to about 1000° C., preferably at about 850°C.

[0062] The p-type cladding layer 9 and the p-type contact layer 11 areso formed under the condition setting the hydrogen concentration of thecarrier gas to the low level (H₂ content: about 1% to about 5%) as toactivate the Mg dopant with no heat treatment in an N₂ atmosphere. Thus,the p-type cladding layer 9 and the p-type contact layer 11 can beformed as p-type semiconductor layers having high carrierconcentrations. Thereafter the SiN layers (not shown) are removed fromthe p-type cladding layer 9, thereby forming the through holes 11 a inthe p-type contact layer 11 as shown in FIG. 2.

[0063] Thereafter the ohmic electrode layer of about 2 nm in thicknessconsisting of the Ni layer, the Pd layer or the Pt layer, the oxidetransparent electrode layer of ITO having the thickness of about 200 nm,the metal reflecting layer of about 1 μm in thickness consisting of theAl layer, the Ag layer or the Rh layer, the barrier electrode consistingof the Pt layer or the Ti layer and the pad electrode consisting of theAu layer or the Au—Sn layer are successively formed on the upper surfaceof the p-type contact layer 11 by vacuum evaporation or the like to fillup the through holes 11 a of the p-type contact layer 11, therebyforming the p-side electrode 12. Further, the ohmic electrode layerconsisting of the Al layer, the barrier electrode consisting of the Ptlayer or the Ti layer and the pad electrode consisting of the Au layeror the Au—Sn layer are successively formed on the region of about 50 μmin width along the outer peripheral portion of the back surface of then-type GaN substrate 1 by vacuum evaporation or the like, therebyforming the n-side electrode 16. The light-emitting diode of thelight-emitting device 10 according to the first embodiment is formed inthe aforementioned manner.

[0064] Finally, the plano-concave lens 50 consisting of the materialsuch as n-type SIC, n-type AlN or p-type diamond having excellentthermal conductivity and electrical conductivity is welded to the backsurface of the n-type GaN substrate 1 through the n-side electrode 16while directing the planar side of the plano-concave lens 50 toward then-type GaN substrate 1. The light-emitting device 10 according to thefirst embodiment is formed in the aforementioned manner.

[0065] According to the first embodiment, as hereinabove described, theinterval D (see FIG. 2) between the through holes 11 a of the p-typecontact layer 11 is set to about {fraction (4/3)}^(1/2) times theemission wavelength λ in the p-type cladding layer 9 while filling upthe aforementioned through holes 11 a with the ohmic electrode layer andthe oxide transparent electrode layer constituting the p-side electrode12, whereby the p-type contact layer 11 can function as atwo-dimensional photonic crystal having a dielectric constantperiodically modulated with respect to the in-plane direction. Further,the p-type contact layer 11 having the aforementioned structure is soformed on the plane parallel to the back surface of the GaN substrate 1serving as the light-emitting surface of the light-emitting diode thatthe light emitted from the light-emitting diode is parallelizedperpendicularly to the light-emitting surface, whereby light extractionefficiency can be improved. In addition, the plano-concave lens 50 is soprovided on the aforementioned light-emitting surface that the parallellight emitted in the direction perpendicular to the aforementionedlight-emitting surface can be easily diffused into various directions bythe concave surface of the plano-concave lens 50. Consequently, thelight-emitting diode can be improved in light extraction efficiency, andcan emit diffused light.

[0066] According to the first embodiment, the plano-concave lens 50 ismade of the material such as n-type SiC, n-type AlN or p-type diamondhaving excellent thermal conductivity so that heat generated in thelight-emitting diode can be easily dissipated. Consequently, thelight-emitting device 10 can be driven with larger current, whereby theintensity of the emitted light can be improved. When a radiation partsuch as a radiation fin is mounted on the plano-concave lens 50, theheat can be further easily dissipated.

[0067] According to the first embodiment, further, the plano-concavelens 50 is made of the material such as n-type SiC having electricalconductivity while the n-side electrode 16 of the light-emitting diodeis formed in close contact with the plano-concave lens 50, whereby thelight-emitting diode and the plano-concave lens 50 can be electricallyconnected with each other. Thus, the plano-concave lens 50 can be formedwith the electrode of the light-emitting diode, whereby thelight-emitting diode may not be directly wired. Therefore, thelight-emitting diode is so easy to assemble that reliability thereof canbe improved. Further, the light-emitting surface may not be wired sothat no wire blocks the emitted light. Consequently, the intensity ofthe light emitted from the light-emitting diode can be improved.

[0068] When the thickness of the ohmic electrode layer constituting thep-side electrode 12 is reduced in the first embodiment, light absorptioncan be reduced. Further, the oxide transparent electrode layerconstituting the p-side electrode 12 can inhibit the ohmic electrodelayer and the metal reflecting layer constituting the p-side electrode12 from reacting with each other. In addition, the barrier electrodeconstituting the p-side electrode 12 can inhibit the metal reflectinglayer and the pad electrode constituting the p-side electrode 12 fromreacting with each other. Further, the barrier electrode constitutingthe n-side electrode 16 can inhibit the ohmic electrode layer and thepad electrode constituting the n-side electrode 16 from reacting witheach other.

Second Embodiment

[0069] Referring to FIGS. 3 and 4, a light-emitting device 20 accordingto a second embodiment of the present invention is formed with a portion(two-dimensional photonic crystal) having a periodically modulateddielectric constant on the back surface (light-emitting surface),dissimilarly to the aforementioned first embodiment. The light-emittingdevice 20 according to the second embodiment includes a light-emittingdiode and a plano-concave lens 50.

[0070] In the light-emitting diode of the light-emitting device 20according to the second embodiment, an n-type multilayer reflector 25obtained by alternately stacking 10 single-crystalline n-typeAl_(0.2)Ga_(0.8)N layers, doped with Si, each having a thickness ofabout 40 nm and 10 single-crystalline n-type GaN layers, doped with Si,each having a thickness of about 40 nm is formed on the upper surface ofa single-crystalline n-type GaN layer 24 doped with Si. An n-typecladding layer 26 of single-crystalline n-type Al_(0.1)Ga_(0.9)N, dopedwith Si, having a thickness of about 0.15 μm is formed on the n-typemultilayer reflector 25. A single quantum well (SQW) active layer 27having an SQW structure consisting of a single-crystalline undopedGa_(0.8)In_(0.2)N well layer having a thickness of about 5 nm is formedon the n-type cladding layer 26.

[0071] A protective layer 28 of single-crystalline undoped GaN having athickness of about 10 nm and a p-type cladding layer 29 ofsingle-crystalline p-type Al_(0.1)Gao_(0.9)N, doped with Mg, having athickness of about 0.15 μm are formed on the SQW active layer 27 in thisorder. A p-type multilayer reflector 30 obtained by alternately stacking10 single-crystalline p-type Al_(0.2)Ga_(0.8)N layers, doped with Mg,each having a thickness of about 40 nm and 10 single-crystalline p-typeGaN layers, doped with Mg, each having a thickness of about 40 nm isformed on the p-type cladding layer 29. A p-type contact layer 31 ofsingle-crystalline p-type Ga_(0.95)In_(0.05)N, doped with Mg, having athickness of about 30 nm is formed on the p-type multilayer reflector30.

[0072] A p-side electrode 32 is formed on the upper surface of thep-type contact layer 31. This p-side electrode 32 is constituted of anohmic electrode layer of about 2 nm in thickness consisting of an Nilayer, a Pd layer or a Pt layer, an oxide transparent electrode layer ofITO having a thickness of about 200 nm, a metal reflecting layer ofabout 1 μm in thickness consisting of an Al layer, an Ag layer or an Rhlayer, a barrier electrode consisting of a Pt layer or a Ti layer and apad electrode consisting of an Au layer or an Au—Sn layer in ascendingorder.

[0073] A support substrate 33 having a thickness of about 200 μm toabout 1 mm is formed on the upper surface of the p-side electrode 32.This support substrate 33 consists of a p-type diamond substrate, ann-type SiC substrate or a polycrystalline AlN substrate. Electrodes 37and 38 each consisting of an Al layer, a Pt payer and an Au layersuccessively stacked from the side closer to the support substrate 33are formed on the front and back surfaces of the support substrate 33respectively. The support substrate 33 is bonded to the p-side electrode32 through the electrode 37.

[0074] According to the second embodiment, a metal layer 34 of Al havinga thickness of about 50 nm is formed on the back surface of the n-typeGaN layer 24. As shown in FIG. 4, the metal layer 34 is formed thereinwith a plurality of circular through holes 34 a, each having a diameterof about 120 nm, arranged in a two-dimensional square lattice at aninterval (D) of about 190 nm substantially equal to the emissionwavelength λ in the p-type cladding layer 29. The metal layer 34 havingthe through holes 34 a is an example of the “portion having a dielectricconstant periodically modulated with respect to the in-plane directionof said plane substantially parallel to said light-emitting surface” inthe present invention. The interval (D) is designed assuming that thepeak emission wavelength λ of light emitted from an emission layer (SQWactive layer 27) is about 440 nm and the refractive index of anitride-based semiconductor is 2.3. An n-side electrode 35 consisting ofan oxide transparent conductive film such as an ITO film is formed onthe back surface of the metal layer 34, to fill up the through holes 34a of the metal layer 34. A pad electrode 36 consisting of an Au layer oran Au—Sn layer is formed on a region of about 50 μm in width along theouter peripheral portion of the back surface of the n-side electrode 35.The light-emitting diode of the light-emitting device 20 according tothe second embodiment has the aforementioned structure.

[0075] According to the second embodiment, the plano-concave lens 50 ofa material such as n-type SiC, n-type AlN or p-type diamond havingexcellent thermal conductivity and electrical conductivity is welded tothe back surface of the pad electrode 36 of the light-emitting diodewhile directing the planar side thereof toward the n-side electrode 35.The plano-concave lens 50 is an example of the “member for diffusinglight emitted from said light-emitting diode” or “means for diffusinglight emitted from said light-emitting diode” in the present invention.The aforementioned light-emitting diode and the plano-concave lens 50constitute the light-emitting device 20 according to the secondembodiment shown in FIG. 3.

[0076] In the aforementioned light-emitting device 20 according to thesecond embodiment, the back surface of the n-side electrode 35 serves asa light-emitting surface emitting light along arrow in FIG. 3.

[0077] A process of fabricating the light-emitting device 20 accordingto the second embodiment is described with reference to FIGS. 3 to 5.

[0078] First, a semiconductor substrate 21 of GaP, GaAs or Si having asurface consisting of a (111) plane (or a Ga plane) is prepared as shownin FIG. 5. A selective growth mask 22 of SiO₂ or SiN, interspersedlyhaving striped openings or hexagonal or circular openings is formed onthe upper surface of the semiconductor substrate 21. N-typelow-temperature buffer layers 23 of non-single-crystalline n-type GaN,AlGaN or AlN, doped with Si, having a thickness of about 10 nm to about50 nm are formed on surface portions of the semiconductor substrate 21exposed between the openings of the selective growth mask 22 with sourcegas consisting of NH₃, TMGa and TMAl and dopant gas of SiH₄ whilekeeping the temperature of the semiconductor substrate 21 at about 400°C. to about 700° C.

[0079] Then, the n-type GaN layer 24 is grown on the n-typelow-temperature buffer layers 23 with carrier gas consisting of an H₂/N₂gas mixture containing about 50% of H₂, source gas consisting of NH₃ andTMGa and dopant gas consisting of SiH₄ at a growth rate of about 3 μm/hwhile keeping the temperature of the semiconductor substrate 21 at about1000° C. to about 1200° C., preferably at about 1150° C.

[0080] Then, the n-type multilayer reflector 25 obtained by alternatelystacking the 10 single-crystalline n-type Al_(0.2)Ga_(0.8)N layers,doped with Si, each having the thickness of about 40 nm and the 10single-crystalline n-type GaN layers, doped with Si, each having thethickness of about 40 nm is grown on the n-type GaN layer 24 withcarrier gas consisting of an H₂/N₂ gas mixture containing about 1% toabout 3% of H₂, source gas consisting of NH₃, TMGa and TMAl and dopantgas consisting of SiH₄ at a growth rate of about 3 μm/h while keepingthe temperature of the semiconductor substrate 21 at about 1000° C. toabout 1200° C., preferably at about 1150° C.

[0081] Then, the n-type cladding layer 26 of single-crystalline n-typeAl_(0.1)Ga_(0.9)N, doped with Si, having the thickness of about 0.15 μmis formed on the n-type multilayer reflector 25 with carrier gasconsisting of an H₂/N₂ gas mixture containing about 1% to about 3% ofH₂, source gas consisting of NH₃, TMGa and TMAl and dopant gasconsisting of SiH₄ at a growth rate of about 3 μm/h while keeping thetemperature of the semiconductor substrate 21 at about 1000° C. to about1200° C., preferably at about 1150° C.

[0082] Then, the SQW active layer 27 consisting of thesingle-crystalline undoped Ga_(0.8)In_(0.2)N well layer having thethickness of about 5 nm is formed on the n-type cladding layer 26 withcarrier gas consisting of an H₂/N₂ gas mixture containing about 1% toabout 5% of H₂ and source gas consisting of NH₃, TEGa and TMIn at agrowth rate of about 0.4 nm/s while keeping the temperature of thesemiconductor substrate 21 at about 700° C. to about 1000° C.,preferably at about 850° C. In continuation, the protective layer 28 ofsingle-crystalline undoped GaN having the thickness of about 10 nm isgrown at a growth rate of about 0.4 nm/s.

[0083] Then, the p-type cladding layer 29 of single-crystalline p-typeAl_(0.1)Ga_(0.9)N, doped with Mg, having the thickness of about 0.15 μmis formed on the protective layer 28 with carrier gas consisting of anH₂/N₂ gas mixture containing about 1% to about 3% of H₂, source gasconsisting of NH₃, TMGa and TMAl and dopant gas consisting of Cp₂Mg at agrowth rate of about 3 μm/h while keeping the temperature of thesemiconductor substrate 21 at about 1000° C. to about 1200° C.,preferably at about 1150° C.

[0084] Then, the p-type multilayer reflector 30 obtained by alternatelystacking the 10 single-crystalline p-type Al_(0.2)Ga_(0.8)N layers,doped with Mg, each having the thickness of about 40 nm and the 10single-crystalline p-type GaN layers, doped with Mg, each having thethickness of about 40 nm is formed on the p-type cladding layer 29 withcarrier gas consisting of an H₂/N₂ gas mixture containing about 1% toabout 3% of H₂, source gas consisting of NH₃, TMGa and TMAl and dopantgas consisting of Cp₂Mg at a growth rate of about 3 μm/h while keepingthe temperature of the semiconductor substrate 21 at about 1000° C. toabout 1200° C., preferably at about 1150° C.

[0085] The p-type cladding layer 29 and the p-type multilayer reflector30 are so formed under the condition setting the hydrogen concentrationof the carrier gas to the low level (H₂ content: about 1% to about 3%)as to activate the Mg dopant with no heat treatment in an N₂ atmosphere.Thus, the p-type cladding layer 29 and the p-type multilayer reflector30 can be formed as p-type semiconductor layers having high carrierconcentrations.

[0086] Then, a contact layer 31 of undoped single-crystallineGa_(0.95)In_(0.05)N having a thickness of about 30 nm is formed on thep-type multilayer reflector 30 with carrier gas consisting of an H₂/N₂gas mixture containing about 1% to about 5% of H₂ and source gasconsisting of NH₃, TEGa and TMIn at a growth rate of about 0.4 nm/swhile keeping the temperature of the semiconductor substrate 21 at about700° C. to about 1000° C., preferably at about 850° C.

[0087] Then, annealing is performed in an N₂ atmosphere while keepingthe temperature of the semiconductor substrate 21 at about 400° C. toabout 900° C., preferably at about 800° C., thereby desorbing hydrogenfrom the contact layer 31. Thus, the hydrogen concentration in thecontact layer 31 is reduced to not more than about 5×10¹⁸ cm. ThereafterMg is ion-implanted into the contact layer 31 at an implantation rate ofabout 1×10¹⁸ cm³ to about 1×10¹⁹ cm³, and annealing is performed in anN₂ atmosphere at about 800° C., thereby converting the contact layer 31to a p-type layer.

[0088] Thereafter the p-side electrode 32 constituted of the ohmicelectrode layer of about 2 nm in thickness consisting of the Ni layer,the Pd layer or the Pt layer, the oxide transparent electrode layer ofITO having the thickness of about 200 nm, the metal reflecting layer ofabout 1 μm in thickness consisting of the Al layer, the Ag layer or theRh layer, the barrier electrode consisting of the Pt layer or the Tilayer and the pad electrode consisting of the Au layer or the Au—Snlayer in ascending order is formed on the upper surface of the contactlayer 31 by vacuum evaporation or the like.

[0089] The support substrate 33 of p-type diamond, n-type SiC or AlN,having the thickness of about 1 μm, formed with the electrodes 37 and 38of Al, Pt and Au on the front and back surfaces respectively isprepared. The support substrate 33 is bonded to the upper surface of thep-side electrode 32 through the electrode 37.

[0090] Then, the semiconductor substrate 21 is removed by wet etching orthe like, and the selective growth mask 22 and the n-typelow-temperature buffer layers 23 are thereafter removed by polishing orthe like, thereby exposing the back surface of the n-type GaN layer 24.

[0091] As shown in FIG. 3, the metal layer 34 of Al having the thicknessof about 50 nm is formed on the exposed back surface of the n-type GaNlayer 24 by vacuum evaporation or the like. Thereafter the circularthrough holes 34 a of about 120 nm in diameter arranged in atwo-dimensional square lattice at the interval (D) of about 190 nmsubstantially equal to the emission wavelength λ in the p-type claddinglayer 29 are formed in the metal layer 34 as shown in FIG. 4, through aprocess similar to that for forming the through holes 11 a of the p-typecontact layer 11 in the aforementioned first embodiment.

[0092] Then, the n-side electrode 35 consisting of the oxide transparentconductive film such as an ITO film is formed on the back surface of themetal layer 34, to fill up the through holes 34 a of the metal layer 34.The pad electrode 36 consisting of the Au layer or the Au—Sn layer isformed on the region of about 50 μm in width along the outer peripheralportion of the back surface of the n-side electrode 35. Thelight-emitting diode of the light-emitting device 20 according to thesecond embodiment is formed in the aforementioned manner.

[0093] Then, the plano-concave lens 50 of the material such as n-typeSiC, N-type AlN or p-type diamond having excellent thermal conductivityand electrical conductivity is welded to the back surface of the n-sideelectrode 35 through the pad electrode 36 while directing the planarside toward the n-side electrode 35. Thus, the light-emitting device 20according to the second embodiment consisting of the light-emittingdiode and the plano-concave lens 50 is formed as shown in FIG. 3.

[0094] According to the second embodiment, as hereinabove described, theinterval D (see FIG. 4) between the through holes 34 a of the metallayer 34 is set to be substantially equal to the emission wavelength Ain the p-type cladding layer 29 while filling up the aforementionedthrough holes 34 a with the oxide transparent conductive filmconstituting the n-side electrode 35, whereby the metal layer 34 canfunction as a two-dimensional photonic crystal having a dielectricconstant periodically modulated with respect to the in-plane direction.Further, the metal layer 34 having the aforementioned structure is soformed on the plane parallel to the back surface of the n-side electrode35 serving as the light-emitting surface of the light-emitting diodethat the light emitted from the light-emitting diode is parallelizedperpendicularly to the light-emitting surface, whereby light extractionefficiency can be improved. In addition, the plano-concave lens 50 is soprovided on the aforementioned light-emitting surface that the parallellight emitted in the direction perpendicular to the aforementionedlight-emitting surface can be easily diffused into various directions.Consequently, the light-emitting device 20 can be improved in lightextraction efficiency, and can emit diffused light.

Third Embodiment

[0095] Referring to FIG. 6, a third embodiment of the present inventionis described with reference to an illuminator 40 including alight-emitting diode 41 constituting a light-emitting device 10 similarto that according to the first embodiment.

[0096] The illuminator 40 according to the third embodiment employs thelight-emitting diode 41 formed by removing a plano-concave lens 50 fromthe light-emitting device 10 similar to that according to the firstembodiment shown in FIG. 1. The light-emitting diode 41 is bonded to theinner bottom surface of a light-emitting device package 42 of aheat-conductive material such as Cu with a welding material such asAu—Sn solder while directing its light-emitting surface upward. Ann-side electrode (not shown) and a p-side electrode (not shown) of thelight-emitting diode 41 are electrically connected with terminals 43 ofthe light-emitting device package 42 by wire bonding.

[0097] A fluorescent body 44 is arranged on an upper opening surface ofthe light-emitting device package 42. An insulating plano-concave lens55 of glass, quartz or resin is arranged on the upper surface of thefluorescent body 55.

[0098] According to the third embodiment, as hereinabove described, thefluorescent body 44 is so set between the light-emitting surface and theplano-concave lens 55 as to scatter light parallelly emitted from thelight-emitting diode 41 perpendicularly to the light-emitting surface,whereby diffused light can be easily obtained. Further, theplano-concave lens 55 also diffuses the emitted light, whereby thediffused light can be more easily obtained. The light-emitting diode 41made of a nitride-based semiconductor emits high-energy light at a shortwavelength in the blue to ultraviolet range, for irradiating thefluorescent body 44 with this light. Thus, the wavelength of the emittedlight can be efficiently converted to a different wavelength with thefluorescent body 44, whereby white light suitable for illumination canbe obtained when various types of fluorescent bodies are with eachother.

Fourth Embodiment

[0099] Referring to FIG. 7, a light-emitting device 60 according to afourth embodiment of the present invention employs a convex mirror 65 inplace of the plano-concave lens 50 employed in the aforementioned secondembodiment. The remaining structure of the light-emitting device 60according to the fourth embodiment is similar to that of thelight-emitting device 20 according to the aforementioned secondembodiment.

[0100] The light-emitting device 60 according to the fourth embodimentis formed by removing a plano-concave lens from a light-emitting devicesimilar to the light-emitting device 20 according to the secondembodiment shown in FIG. 3. In other words, a light-emitting diode ofthe light-emitting device 60 according to the fourth embodiment includesa metal layer 34 functioning as a two-dimensional photonic crystalhaving a dielectric constant periodically modulated with respect to thein-plane direction. The convex mirror 65 is arranged at a prescribedinterval from a light-emitting surface of the light-emitting diode, tobe opposed to the light-emitting diode. This convex mirror 65 is formedby coating the convex surface of resin or glass with a reflecting filmof Al or Ag. This convex mirror 65 is an example of the “member fordiffusing light emitted from said light-emitting diode” or “means fordiffusing light emitted from said light-emitting diode” in the presentinvention.

[0101] In the light-emitting device 60 according to the fourthembodiment, the metal layer 34 can function as the two-dimensionalphotonic crystal having the dielectric constant periodically modulatedwith respect to the in-plane direction similarly to that in theaforementioned second embodiment, whereby the light emitted from thelight-emitting diode can be parallelized perpendicularly to thelight-emitting surface. Thus, light extraction efficiency can beimproved.

[0102] In the light-emitting device 60 according to the fourthembodiment, further, the convex mirror 65 is arranged oppositely to thelight-emitting surface of the light-emitting diode as hereinabovedescribed, whereby the light emitted from the light-emitting diode canbe reflected and diffused by the convex mirror 65.

Fifth Embodiment

[0103] Referring to FIGS. 8 and 9, plano-concave lenses 72 a andlight-emitting diodes 71 are two-dimensionally (planarly) arranged inthe form of an array (matrix) in a light-emitting device 70 according toa fifth embodiment of the present invention.

[0104] In the light-emitting device 70 according to the fifthembodiment, a plurality of light-emitting diodes 71 are arranged on alens member 72 of polycarbonate, for example, in the form of a matrix(array) in plane, as shown in FIG. 8. More specifically, 324light-emitting diodes 71 are arranged in the form of a 18 by 18 matrix.Each of the light-emitting diodes 71 has a structure obtained byremoving a plano-concave lens from a light-emitting diode similar tothat according to the first or second embodiment shown in FIG. 1 or 3.In other words, each of the light-emitting diodes 71 of thelight-emitting device 70 according to the fifth embodiment includes ap-type contact layer 11 (see FIG. 1) or a metal layer 34 (see FIG. 3)functioning as a two-dimensional photonic crystal having a dielectricconstant periodically modulated with respect to the in-plane direction.

[0105] The lens member 72 is constituted of a plurality of plano-concavelenses 72 a arranged in the form of a matrix (array) in plane. As shownin FIG. 8, the plano-concave lenses 72 a are arranged in the form of a 3by 3 matrix (9 plano-concave lenses 72 a in total). Each plano-concavelens 72 a is arranged at a ratio of one to a plurality of (36)light-emitting diodes 71. The planar surfaces of the plano-concavelenses 72 a are formed with transparent electrodes of ITO. Thetransparent electrodes excite the light-emitting diodes 71 through ohmicelectrodes of metal. The plano-concave lenses 72 a are examples of the“member for diffusing light emitted from said light-emitting diode” or“means for diffusing light emitted from said light-emitting diode” inthe present invention.

[0106] According to the fifth embodiment, as hereinabove described, theplano-concave lenses 72 a and the light-emitting diodes 71 are sotwo-dimensionally (planarly) arranged in the form of an array (matrix)that the sizes of regions for emitting light can be increased. Thus, thelight-emitting device 70 can be easily used as a light source forillumination or the like.

[0107] According to the fifth embodiment, further, light parallelizedperpendicularly to a light-emitting surface can be obtained through thep-type contact layers 11 or the metal layers 34 functioning astwo-dimensional photonic crystals similarly to the first or secondembodiment, whereby light extraction efficiency can be improved and theparallelized light can be diffused through the plano-concave lenses 72a.

[0108] The remaining effects of the fifth embodiment are similar tothose of the aforementioned first or second embodiment.

Sixth Embodiment

[0109] Referring to FIG. 10, a light-emitting device 80 according to asixth embodiment of the present invention employs a diffusion sheet 82consisting of a translucent film dispersively containing a lightdiffusing agent 82 a consisting of transparent particulates.

[0110] According to the sixth embodiment, a transparent electrode of ITOis formed on the surface of the translucent diffusion sheet 82, as shownin FIG. 10. A plurality of light-emitting diodes 81 are arranged on thesurface of the transparent electrode formed on the diffusion sheet 82 inthe form of a matrix (array) in plane through an ohmic electrode ofmetal. In this case, light-emitting surfaces of the light-emittingdiodes 81 are bonded to the surface of the diffusion sheet 82. Eachlight-emitting diode 81 has a structure obtained by removing aplano-concave lens from a light-emitting diode similar to that accordingto the first or third embodiment shown in FIG. 1 or 3. In other words,each light-emitting diode 81 of the light-emitting device 60 accordingto the sixth embodiment includes a p-type contact layer 11 (see FIG. 1)or a metal layer 34 (see FIG. 3) functioning as a two-dimensionalphotonic crystal having a dielectric constant periodically modulatedwith respect to the in-plane direction. Thus, the light-emitting diode81 emits light parallelized perpendicularly to the light-emittingsurface, thereby improving light extraction efficiency.

[0111] According to the sixth embodiment, the light diffusing agent 82 aconsisting of substantially spherical particulates of about 1 μm toabout 20 μm in grain size is added into the diffusion sheet 82constituting of glass or transparent plastic. This light diffusing agent82 a consists of an inorganic material such as SiN_(x), TiO₂ or Al₂O₃ oran organic material such as polymethyl methacrylate, polyacrylonitrile,polyester, silicone, polyethylene, epoxy, a melamine-formaldehydecondensate, a benzoguanamine-formaldehyde condensate or amelamine-benzoguanamine-formaldehyde condensate. When the diffusionsheet 82 is constituted of a transparent plastic film and the lightdiffusing agent 82 a is constituted of amelamine-benzoguanamine-formaldehyde condensate, for example, the weightratio of the plastic film to the melamine-benzoguanamine-formaldehydecondensate is about 30:70.

[0112] In the light-emitting device 80 according to the sixthembodiment, as hereinabove described, the light-emitting diodes 81 areso two-dimensionally (planarly) arranged in the form of an array(matrix) that the sizes of regions emitting light can be increased.Thus, the light-emitting device 80 can be easily used as a light sourcefor illumination or the like.

[0113] According to the sixth embodiment, further, the light-emittingsurfaces of the light-emitting diodes 81 are bonded to the diffusionsheet 82 containing the light diffusing agent 82 a so that the lightemitted from the light-emitting diodes 81 arranged in the form of amatrix can be easily diffused.

[0114] The remaining effects of the sixth embodiment are similar tothose of the aforementioned first or second embodiment.

Seventh Embodiment

[0115] Referring to FIG. 11, a light-emitting device 90 according to aseventh embodiment of the present invention employs a diffusion sheet 93formed with fine corrugation 93 a and 93 b on the front and backsurfaces thereof respectively as a member diffusing light emitted fromlight-emitting diodes 91, dissimilarly to the aforementioned sixthembodiment.

[0116] According to the seventh embodiment, the fine corrugation 93 aand 93 b are formed on the front and back surfaces of the translucentdiffusion sheet 93 consisting of a glass sheet or a transparent plasticfilm, as shown in FIG. 11. In the fine corrugation 93 a and 93 b, thepitch (interval) between adjacent recess portions is set to about 200 nmto about 2000 nm or to about 2 μm to about 100 am. When the pitch(interval) between the adjacent recess portions is about 200 nm to about2000 nm, this interval corresponds to a value equivalent to or severaltimes the emission wavelength, whereby the fine corrugation 93 a and 93b diffuse light by a diffraction effect. When the pitch (interval)between the adjacent recess portions is about 2 μm to about 100 μm, thecorrugation 93 a and 93 b refract light thereby diffusing the light.

[0117] A plurality of light-emitting diodes 91 are arranged on thesurface of a support plate 92 consisting of a material such as Al havinghigh reflectance and excellent heat radiability in the form of a matrix(array) in plane. In this case, surfaces of the light-emitting diodes 91opposite to the light-emitting surfaces are bonded to the surface of thesupport plate 92. The diffusion sheet 93 is arranged at a prescribedinterval from the light-emitting diodes 91, to be opposed to thelight-emitting surfaces of the light-emitting diodes 91 bonded to thesurface of the support plate 92.

[0118] Each light-emitting diode 91 has a structure obtained by removinga plano-concave lens 50 from a light-emitting diode similar to thataccording to the first or third embodiment shown in FIG. 1 or 3. Inother words, each light-emitting diode 91 of the light-emitting device90 according to the seventh embodiment includes a p-type contact layer11 (see FIG. 1) or a metal layer 34 (see FIG. 3) functioning as atwo-dimensional photonic crystal having a dielectric constantperiodically modulated with respect to the in-plane direction. Thus, thelight-emitting diode 91 emits light parallelized perpendicularly to thelight-emitting surface, thereby improving light extraction efficiency.

[0119] In the light-emitting device 90 according to the seventhembodiment, as hereinabove described, the light-emitting diodes 91 areso two-dimensionally (planarly) arranged in the form of an array(matrix) that the sizes of regions for emitting light can be increased.Thus, the light-emitting device 90 can be easily used as a light sourcefor illumination or the like.

[0120] According to the seventh embodiment, further, the light-diffusingdevice 90 provided with the diffusion sheet 93 having the finecorrugation 93 a and 93 b on the front and back surfaces thereof caneasily diffuse the light emitted from the light-emitting diodes 91arranged in the form of a matrix.

[0121] The remaining effects of the seventh embodiment are similar tothose of the aforementioned first or second embodiment.

Eighth Embodiment

[0122] Referring to FIG. 12, an eighth embodiment of the presentinvention is described with reference to an illuminator 100 employing alight-emitting device 70 similar to that according to the aforementionedfifth embodiment.

[0123] In the illuminator 100 according to the eighth embodiment, thelight-emitting device 70 having plano-concave lenses 72 a andlight-emitting diodes 71, similar to those according to theaforementioned fifth embodiment, two-dimensionally (planarly) arrangedin the form of an array (matrix) is mounted on the surface of areflector 101 of Al also serving as a radiator plate, as shown in FIG.12. More specifically, a surface of the light-emitting device 70opposite to light-emitting surfaces of the light-emitting diodes 71 ismounted on the reflector 101. A concave glass plate 102 is mounted toenclose the light-emitting device 70. A fluorescent layer 103 for whiteillumination is formed on the inner side of the concave glass plate 102.

[0124] The fluorescent layer 103 for white illumination is formed bymixing fluorescent materials of four emission colors of blue, green, redand yellow, for example, with each other. In this case, the bluefluorescent material is prepared from BaMgAl₁₇O₁₀:Eu or(Sr,Ca,Ba,Mg)₁₀(PO₄)₆Cl₂:Eu, and the green fluorescent material isprepared from ZnS:Cu,Al. The red fluorescent material is prepared fromY₂O₂S:Eu, and the yellow fluorescent material is prepared from(Y,Gd)₃Al₅O₁₂:Ce. Terminals (not shown) for exciting the light-emittingdevice 70 are set on the reflector 101.

[0125] In the illuminator 100 according to the eighth embodiment, ashereinabove described, the light-emitting diodes 71 including the p-typecontact layers 11 or the metal layers 34 functioning as two-dimensionalphotonic crystals are so employed that light parallelizedperpendicularly to the light-emitting surfaces can be obtained, wherebylight extraction efficiency of the light-emitting diodes 71 can beimproved. Further, the plano-concave lenses 72 a can diffuse theparallel light emitted from the light-emitting diodes 71, wherebydiffused light suitable for illumination can be obtained. In addition,the plano-concave lenses 72 a and the light-emitting diodes 71 aretwo-dimensionally (planarly) arranged on the light-emitting device 70 inthe form of an array (matrix) so that the sizes of regions emittinglight can be increased, whereby brightness necessary for the illuminator100 can be easily obtained.

[0126] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

[0127] For example, the plano-concave lens(es) 50 or 72 a, the convexmirror 65, the diffusion sheet 82 including the light diffusing agent 82a or the diffusing sheet 93 having the fine corrugation 93 a and 93 b isemployed as the member(s) (means) diffusing the light emitted from thelight-emitting diode(s) according to the present invention in each ofthe aforementioned embodiments, the present invention is not restrictedto this but a lens, a mirror or a diffraction grating having a differentshape may alternatively be employed as the member (means) diffusingemitted light.

[0128] While each of the aforementioned embodiments employs the photoniccrystal(s) as the portion(s) having the periodically modulateddielectric constant according to the present invention, the presentinvention is not restricted to this but a structure other than thephotonic crystal may alternatively be employed as the portion having theperiodically modulated dielectric constant.

[0129] While in the light-emitting device in the aforementioned fourthembodiment a single convex mirror is arranged to a single light-emittingdiode, the present invention is not restricted to this but the convexmirror may alternatively be arranged at ratio of one to a plurality oflight-emitting diodes or a plurality of convex mirrors andlight-emitting diodes may alternatively be arranged in the form of anarray (matrix).

[0130] While the light-emitting device 70 similar to that according tothe fifth embodiment is built into the illuminator 100 according to theeighth embodiment, the present invention is not restricted to this but alight-emitting device similar to that according to the sixth or seventhembodiment may alternatively be built into the illuminator 100 accordingto the eighth embodiment.

[0131] In each of the first and second embodiments, a transparentelectrode may be formed on the planar side of the plano-concave lens 50of an insulator such as glass, for welding the light-emitting diode tothis plane.

What is claimed is:
 1. A light-emitting device comprising: alight-emitting diode; a portion, formed on a plane substantiallyparallel to a light-emitting surface of said light-emitting diode,having a dielectric constant periodically modulated with respect to thein-plane direction of said plane substantially parallel to saidlight-emitting surface; and a member provided on the side of saidlight-emitting surface of said light-emitting diode for diffusing lightemitted from said light-emitting diode.
 2. The light-emitting deviceaccording to claim 1, wherein said portion having said periodicallymodulated dielectric constant is constituted by periodically arrangingmaterials having different dielectric constants.
 3. The light-emittingdevice according to claim 1, wherein said portion having saidperiodically modulated dielectric constant consists of a photoniccrystal.
 4. The light-emitting device according to claim 1, wherein saidmember diffusing emitted said light is conductive.
 5. The light-emittingdevice according to claim 4, wherein said conductive member diffusingsaid emitted light is formed to be in contact with a portion of saidlight-emitting diode provided on the light-emitting side.
 6. Thelight-emitting device according to claim 4, wherein said conductivemember diffusing said emitted light consists of at least one materialselected from a group consisting of n-type SiC, n-type AlN and p-typediamond.
 7. The light-emitting device according to claim 1, wherein saidmember diffusing emitted said light includes a lens.
 8. Thelight-emitting device according to claim 7, wherein said memberdiffusing said emitted light includes a concave lens.
 9. Thelight-emitting device according to claim 8, wherein said concave lensincludes a plano-concave lens having a flat first surface and a concavesecond surface.
 10. The light-emitting device according to claim 1,wherein said member diffusing emitted said light includes a convexmirror.
 11. The light-emitting device according to claim 1, wherein saidmember diffusing emitted said light includes a translucent memberdispersively containing a light diffusing agent consisting ofsubstantially transparent particulates.
 12. The light-emitting deviceaccording to claim 1, wherein said member diffusing emitted said lightincludes a translucent member having fine corrugation at least either onthe front surface or on the back surface.
 13. The light-emitting deviceaccording to claim 12, wherein the interval between adjacent projectingportions in said fine corrugation is at least about 200 nm and not morethan about 2000 nm.
 14. The light-emitting device according to claim 12,wherein the interval between adjacent projecting portions in said finecorrugation is at least about 2 μm and not more than about 100 μm. 15.The light-emitting device according to claim 1, further comprising afluorescent body provided between said light-emitting surface and saidmember diffusing emitted said light.
 16. The light-emitting deviceaccording to claim 1, wherein said light-emitting diode includes anemission layer, and said emission layer consists of a nitride-basedsemiconductor.
 17. The light-emitting device according to claim 1,wherein a plurality of said light-emitting diodes are arranged in theform of a matrix in plane.
 18. The light-emitting device according toclaim 17, wherein said member diffusing emitted said light includes alens, and a plurality of said lenses are arranged in the form of amatrix in plane.
 19. A light-emitting device comprising: alight-emitting diode; a portion, formed on a plane substantiallyparallel to a light-emitting surface of said light-emitting diode,having a dielectric constant periodically modulated with respect to thein-plane direction of said plane substantially parallel to saidlight-emitting surface; and means provided on the side of saidlight-emitting surface of said light-emitting diode for diffusing lightemitted from said light-emitting diode.
 20. An illuminator comprising alight-emitting device including: a light-emitting diode; a portion,formed on a plane substantially parallel to a light-emitting surface ofsaid light-emitting diode, having a dielectric constant periodicallymodulated with respect to the in-plane direction of said planesubstantially parallel to said light-emitting surface; and a memberprovided on the side of said light-emitting surface of saidlight-emitting diode for diffusing light emitted from saidlight-emitting diode.
 21. The illuminator according to claim 20, furthercomprising a fluorescent body arranged at a prescribed interval fromsaid light-emitting device for converting light emitted from saidlight-emitting device to white light.
 22. The illuminator according toclaim 21, wherein said fluorescent body is formed by mixing fluorescentmaterials having a plurality of colors with each other.
 23. Theilluminator according to claim 20, wherein a plurality of saidlight-emitting diodes constituting said light-emitting device arearranged in the form of a matrix in plane.
 24. The illuminator accordingto claim 23, wherein said member diffusing emitted said light includes alens, and a plurality of said lenses are arranged in the form of amatrix in plane.